1. Field of the Invention
Embodiments of the invention generally relate to deposition of a metal layer onto a wafer/substrate. Particularly, the invention relates to electro-chemical deposition systems, integrated with electrolyte analyzing modules, for forming a metal layer on a wafer/substrate. More particularly, the invention relates to a method for measuring the concentration of components, including additives in a plating solution useful in electrochemical deposition systems.
2. Description of the Related Art
The semiconductor industry""s progress in multilevel metallization of topographical interconnect features with diverse pattern densities commonly used in the manufacture of high performance very large scale integration (VLSI) and ultra large-scale integration (ULSI) devices has pushed semiconductor performance ever faster. As the fringes of circuit technology are pressed, the shrinking dimensions of the interconnects in sub-quarter micron and smaller features for the next generation of VLSI and ULSI technologies has placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of semiconductor technology require precise processing of high aspect ratio features, such as vias, contacts, lines, and other interconnects. Reliable formation of these interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
Electro-chemical plating (ECP), originally used in other industries, has been applied in the semiconductor industry as a deposition technique for filling sub-quarter micron features because of its ability to grow the deposited material, such as copper, on a conductive surface and fill even high aspect ratio features substantially free of voids. Typically, a metallic diffusion barrier layer is deposited over a feature surface, followed by the deposition of a conductive metal seed layer. Then, a conductive metal is electro-chemically plated over the seed layer to fill the structure/feature. Finally, the surface of the features are planarized, such as by chemical mechanical polishing (CMP), to define a conductive interconnect feature.
Copper has become the desired metal for semiconductor device fabrication, because of its lower resistivities and significantly higher electromigration resistance as compared to aluminum, and good thermal conductivity. Copper electrochemical plating systems have been developed for semiconductor fabrication of advanced interconnect structures. Typically, copper ECP uses a plating bath/electrolyte including positively charged copper ions in contact with a negatively charged substrate, as a source of electrons, to plate out the copper on the charged substrate.
All ECP electrolytes have both inorganic and organic compounds at low concentrations. Typical inorganics include copper sulfate (CUSO4), sulfuric acid (H2SO4), and trace amounts of chloride (Clxe2x88x92) ions. Typical organics include accelerators, suppressors, and levelers. An accelerator is sometimes called a brightener or anti-suppressor. A suppressor may be a surfactant or wetting agent, and is sometimes called a carrier. A leveler is also called a grain refiner or an over-plate inhibitor.
Although simple in principle, copper plating relies in practice on the use of proper additives in the electrolyte to determine the properties of the copper being deposited. Because of depletion, analysis of the processing additives is required periodically during the plating process. If the concentrations change, or if the additive components get out of balance, the quality of the plated copper deteriorates. Monitoring and control of inorganic and organic additives by chemical analyzers are very important, especially as the technological demands on the copper become more stringent.
Additive control in copper plating is a major scientific and technological challenge. The electrochemical signals, such as electric potential and current, are functions of all the organic additives added, and require detailed analyses to determine the composition of the electrolyte to ensure proper proportions of the components. Conventional analysis is performed by extracting a sample of electrolyte from a test port followed by transferring the sample to a remote chemical analyzer. The electrolyte composition is then adjusted according to the results of the analysis. The analysis must be performed frequently because the concentrations of the various chemicals are in constant flux.
Organic chemical analyzers implementing different electro-analytical principles such as CVS (Cyclic Voltammetric Stripping), CPVS (Cyclic Pulse Voltammetric stripping), and PCGA (Pulsed Cyclic Galvanostatic Analysis) are widely used for the analysis of organic additive concentration in metal plating baths. The organic chemical analyzer is typically coupled to a metal plating apparatus, such as an electrochemical plating (ECP) apparatus for depositing metal films on semiconductor devices. These electro-analytical principles are based on high sensitivity of electrochemical responses, such as over-potential or current, of metal plating processes toward trace amounts of organic additives inside a plating cell/container of the organic chemical analyzer to provide bath additive analysis.
Despite claims that organic chemical analysis performed by various electro-analytical principles can be used as monitoring tools and the availability of CVS, PCGA, and CPVS instruments, many serious questions about additive analysis still arise. This is because in commercial production plating baths, all additives co-exist and can adsorb on the surface of an electrode inside the organic chemical analyzer to affect the quality of the plated metals, resulting in so-called interference effect or matrix effect.
In the implementation of CVS, PCGA, and CPVS principles, different supporting-electrolyte solutions are thus prepared inside the plating cell of the organic chemical analyzer for measuring electrochemical responses to minimize or eliminate the interference effect coming from one type of organic additive on the electrode surface. For example, excess amounts of suppressor solution are mixed with an inorganic virgin make-up solution to make up a supporting-electrolyte solution for analyzing the concentration of an accelerator type additive by a Modified Linear Approximation Technique (MLAT). In addition, a Dilution Titration (DT) method with virgin make-up solutions (VMS) as the supporting-electrolyte solution has been used to analyze the concentration of a suppressor. The VMS solution includes at least three inorganic components, such as charged cations of the metal to be plated, charged anions, an acid or base for adjusting pH and bath electrical resistance, and combinations thereof. In many cases, however, inorganic VMS is not sufficient as the supporting-electrolyte solution, and the analysis accuracy and precision suffer because other types of organic additives in the solution to be tested still exert significant interference to the dependence of the electrochemical responses on the organic additive to be analyzed.
In addition, the foregoing analytical methods are time consuming and limited in terms of the number of analyses being performed and analysis must be repeated continuously to obtain any degree of control, because concentration of organics is changing continuously during the plating operation. For example, the CVS methods cannot measure all different types of organic components independently. Two or more of the organic components have to be analyzed independently of each other prior to finding the information on the concentrations of these two components fed into the analyses of the third component to get reliable and accurate analyses on the concentration of the third component. This severely limited the user""s capability to analyze the concentration of the third component at any desired moment.
For example, in determining the concentration of a leveler, knowledge of the concentrations of all other co-existing components is required before the concentration of the leveler can be determined. Thus, it is difficult to minimize or even eliminate the interference effect to obtain reliable analysis results.
Therefore, a need exists to provide methods for real-time independent analysis of each electrolyte component in a processing system integrated with one or more chemical analyzers.
Embodiments of the invention provide an electro-analytical method for determining the concentration of an organic additive in an acidic or basic metal plating bath using an organic chemical analyzer. The method includes preparing a supporting-electrolyte solution, preparing a testing solution, measuring an electrochemical response of the supporting-electrolyte solution and the testing solution using the organic chemical analyzer, and implementing an electro-analytical technique to determine the concentration of the organic additive in the plating bath from the electrochemical response measurements. The method is performed for independently analyzing one organic additive component in a plating bath containing multi-component organic additives.
In one embodiment, a method for determining the concentration of an accelerator in an unknown plating bath using an organic chemical analyzer is provided, regardless of the knowledge of the concentration of a suppressor, a leveler, or other organic additives, and with minimal interference among organic additives. The supporting-electrolyte solution for determining the accelerator concentration includes a virgin make-up solution, up to about 5 ml/L of the accelerator, brightener, or anti-suppressor, and between about 10 ml/L and about 60 ml/L of a suppressing agent of the plating bath. The testing solution for determining the accelerator concentration includes the supporting-electrolyte solution and a production solution having a dilution aliquot of the plating bath, and optionally at least one volume of a standard solution having known concentration of at least one organic additive for the plating bath.
In another embodiment, a method for determining the concentration of a suppressor in an unknown plating bath using an organic chemical analyzer is provided, regardless of the knowledge of the concentrations of an accelerator, a leveler, or other organic additives, and with minimal interference among organic additives. The supporting-electrolyte solution for determining the suppressor concentration includes a virgin make-up solution of all inorganic substances of the plating bath and up to about 0.5 ml/L of the suppressor, carrier, surfactant, or wetting agent of interest. The testing solution for determining the suppressor concentration includes the supporting-electrolyte solution and at least one volume of a standard solution having known concentration of at least one organic additive for the plating bath.
In another embodiment, a method for determining the concentration of a leveler in an unknown plating bath using an organic chemical analyzer is provided, regardless of the knowledge of the concentrations of an accelerator, a suppressor, or other organic additives, and with minimal interference among organic additives. The supporting-electrolyte solution for determining the leveler concentration includes a virgin make-up solution, up to about 60 ml/L of an accelerator, brightener, or anti-suppressor, and up to about 60 ml/L of a suppressor, carrier, surfactant, or wetting agent except the leveler, over-plate inhibitor, or grain refiner of interest. The testing solution for determining the leveler concentration includes the supporting-electrolyte solution and at least one volume of a standard solution having known concentration of at least one organic additive for the plating bath.